Radar module and antenna device

ABSTRACT

A radar module has an antenna assembly, a plurality of transmitting and receiving assemblies, and a plurality of circulators all mounted on a dielectric substrate. The antenna assembly has a plurality of transmitting and receiving channels including respective planar array antenna elements each composed of a plurality of patches connected to and spaced along a linear distal end portion of a feeder line. The planar array antenna elements are arrayed in a direction substantially perpendicular to the linear distal end portion of the feeder line. The transmitting and receiving assemblies, implemented as monolithic microwave integrated circuits, selectively transmit high-frequency signals to the planar array antenna elements and selectively receive echo signals from the planar array antenna elements. The circulators are associated with the transmitting and receiving channels, respectively, and connect the respective linear distal end portions of the feeder lines to transmission and reception end portions which are connected to the transmitting and receiving assemblies, respectively.

This is a divisional of application Ser. No. 08/611,665, filed on Mar.6, 1996, now U.S. Pat. No. 5,724,042.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radar module and an antenna devicefor an FM millimeter-wave radar alarm system for use on motor vehicles.

2. Description of the Prior Art

One known motor vehicle radar alarm system has an electronicallyscanning planar antenna array as disclosed in U.S. Pat. No. 5,008,678.The disclosed electronically scanning planar antenna array comprises aplurality of transmitting and receiving planar antenna elements, a pairof passive phased arrays such as planar microstrip Butler matrixes, anda pair of electronic switches which are combined to transmit and receivea scanning beam.

The conventional electronically scanning planar antenna array isdisadvantageous in that the passive phased arrays thereof cannot scan arelatively large angular range with the scanning beam. Another problemis that the planar antenna array requires both a transmitting array ofantenna elements dedicated to transmitting radar signals and a receivingarray of antenna elements dedicated to receiving echo signals. Thisimposes limitations on conventional systems which make it difficult toreduce the size of the planar antenna arrays used therein and,especially difficult to install such planar antenna arrays on motorvehicles.

German laid-open publication No. 4307009 discloses an antenna device fora radar module.

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. MTT-26, NO.1, January 1978, shows an MIC Doppler module with output radiationnormal to the substrate plane.

Japanese patent publication No. 57-24968 discloses a microwave IC case.

Japanese laid-open utility model publication No. 1-126714 discloses anantenna device.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a radar module andan antenna device which are capable of scanning a relatively largeangular range with a scanning beam and which are of a small sizesuitable for use particularly on motor vehicles.

According to one aspect of the present invention, there is provided aradar module comprising a dielectric substrate, an antenna assemblymounted on the dielectric substrate, the antenna assembly comprising aplurality of transmitting and receiving channels including respectiveplanar array antenna elements each composed of a plurality of patchesconnected to and spaced along a linear distal end portion of a feederline, the planar array antenna elements being arrayed in a directionsubstantially perpendicular to the linear distal end portion of thefeeder line, a plurality of transmitting and receiving assembliesmounted as monolithic microwave integrated circuits on the dielectricsubstrate, for selectively transmitting high-frequency signals to theplanar array antenna elements and selectively receiving echo signalsfrom the planar array antenna elements, and a plurality of circulatorsmounted on the dielectric substrate and associated with the transmittingand receiving channels, respectively, the circulators connecting therespective linear distal end portions of the feeder lines totransmission and reception end portions which are connected to thetransmitting and receiving assemblies, respectively.

The antenna assembly serves as a primary radiator of a defocusedmultiple-beam antenna. The planar array antenna elements are arranged toradiate respective electromagnetic waves at a predetermined tilt angle,the offset multiple-beam antenna having a secondary radiator positionedclosely to the primary radiator.

According to another aspect of the present invention, there is alsoprovided a radar module comprising a dielectric substrate, a pluralityof planar array antenna elements mounted in respective channels on thedielectric substrate, and a plurality of monolithic microwave integratedcircuits mounted on the dielectric substrate, the monolithic microwaveintegrated circuits including a plurality of transmitting assemblies foramplifying and supplying respective high-frequency signals to the planararray antenna elements, respectively, and a plurality of receivingassemblies for receiving echo signals from the planar array antennaelements and mixing the echo signals with amplified local signalsrelated to the high-frequency signals.

In each of the above radar modules, the planar array antenna elementsare divided into two groups, the planar array antenna elements of one ofthe two groups and the planar array antenna elements of the other of thetwo groups being arranged in an interdigitating pattern and disposed onrespective linear distal end portions of feeder lines belonging to therespective groups and extending in opposite directions that are 180°apart from each other.

Alternatively, the planar array antenna elements may be divided into twogroups, the planar array antenna elements of one of the two groups andthe planar array antenna elements of the other of the two groups beingdisposed on respective linear distal end portions of feeder linesbelonging to the respective groups and extending in opposite directionsthat are 180 apart from each other, and being positioned substantiallyin an end-to-end configuration and staggered with respect to each otherin a direction across the feeder lines.

The high-frequency signals transmitted to the planar array antennaelements comprise frequency-modulated signals, the receiving assembliesincluding mixers for mixing echo signals from the planar array antennaelements with the frequency-modulated signals to thereby produce beatsignals.

The transmitting assemblies include transmission amplifiers foramplifying the high-frequency signals, and the receiving assembliesinclude reception amplifiers for amplifying the local signals. A controlcircuit is provided for selectively operating the transmissionamplifiers and the reception amplifiers.

According to still another aspect of the present invention, there isalso provided an antenna device comprising a dielectric substrate, anarray of antenna elements mounted on the dielectric substrate, each ofthe antenna elements comprising a plurality of patches interconnected ina direction transverse to the array, and a plurality of circulatorsmounted on the dielectric substrate and connected in series to theantenna elements, respectively.

The circulators are arranged in adjacent pairs, the circulators in eachof the pairs being arranged such that DC magnetic fields in mutuallyopposite directions are applied to the circulators, respectively, forrotating signals in mutually opposite directions in the circulators.

The antenna device further comprises a scanning control circuit forswitching the antenna elements in a time-sharing fashion.

According to still another aspect of the present invention, there isprovided an antenna device comprising a dielectric substrate, a primaryradiator comprising an array of antenna elements mounted on thedielectric substrate, each of the antenna elements comprising aplurality of patches interconnected in a direction transverse to thearray, and a plurality of circulators mounted on the dielectricsubstrate and connected in series to the antenna elements, respectively,a secondary radiator for reflecting a beam radiated from the antennaelements, and a holder supporting the primary radiator integrally withthe secondary radiator, with the primary radiator being positionedsubstantially at a focal point of the secondary radiator.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description whenviewed in conjunction with the accompanying drawings which illustrate,by way of example, preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an FM radar system which incorporates an FMradar module according to an embodiment of the present invention;

FIG. 2 is a plan view of the physical structure of the FM radar moduleshown in FIG. 1;

FIG. 3 is an enlarged plan view of one unit of transmitting andreceiving channels of the FM radar module shown in FIG. 2;

FIG. 4 is a perspective view of a FM radar system which incorporates theFM radar module shown in FIG. 1;

FIG. 5 is a diagram showing distances to echo-generating objects thatare detected by the FM radar system which incorporates the FM radarmodule shown in FIG. 1, together with a distribution of bearings coveredby the FM radar system;

FIG. 6 is a diagram illustrative of a tilt angle of planar array antennaelements of the FM radar module shown in FIG. 2; and

FIG. 7 is a plan view of a pattern of planar array antenna elements ofan FM radar module according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows in block form an FM radar system which incorporates an FMradar module according to an embodiment of the present invention.

As shown in FIG. 1, the FM radar system generally comprises an FM radarmodule 10 and a main radar circuit 20. The FM radar system is preferablyinstalled on a motor vehicle (not shown).

The FM radar module 10 comprises a dielectric substrate 11 having anantenna assembly 12 mounted thereon. The antenna assembly 12 comprises aplurality (16 in the illustrated embodiment) of transmitting andreceiving channels A.sup.˜ P disposed on the dielectric substrate 11.The transmitting and receiving channels A.sup.˜ P comprise respectivesmall-size planar array antenna elements 12a.sup.˜ 12p and respectivetransmitting and receiving assemblies. The small-size planar arrayantenna elements 12a.sup.˜ 12p are shared by the transmitting andreceiving assemblies through respective circulators 14a.sup.˜ 14p whichare connected in series with the planar array antenna elements 12a.sup.˜12p, respectively. The transmitting assemblies include respectiveselective transmission amplifiers 15a.sup.˜ 15p, and the receivingassemblies include respective selective reception amplifiers 16a.sup.˜16p and respective mixers 17a.sup.˜ 17p. The transmitting and receivingchannels A.sup.˜ P receive FM (frequency-modulated) signals to betransmitted which are supplied from an FM signal generator 23 in themain radar circuit 20 through a microstrip line MS.

The main radar circuit 20 comprises a CPU (central processing unit) 21,a channel controller 22, an FM signal generator 23, a selector 24, anA/D (analog-to-digital) converter 25, an FFT (fast Fourier transform)circuit 26, and a memory 27.

The FM radar module 10 shown in FIG. 1 has the physical structureillustrated in FIG. 2. The dielectric substrate 11, which is housed in ametallic casing, is made of highly pure alumina ceramic having arelative dielectric constant of 9.7, and supports thereon a plurality of(8 in the illustrated embodiment) MMICs (monolithic microwave integratedcircuits) 13a.sup.˜ 13h.

In order for the FM radar module 10 to provide an installation space forthe 16 circulators 14a.sup.˜ 14p which are relatively large in size, the16 planar array antenna elements 12a.sup.˜ 12p and the correspondingtransmitting and receiving channels A.sup.˜ P including the circulators14a.sup.˜ 14p are divided into two groups. Specifically, the 16 planararray antenna elements 12a.sup.˜ 12p are divided into a group of eightplanar array antenna elements 12a.sup.˜ 12h and a group of eight planararray antenna elements 12i.sup.˜ 12p. The eight planar array antennaelements 12a.sup.˜ 12h of one group and the eight planar array antennaelements 12i.sup.˜ 12p of the other group are arranged ininterdigitating pattern and disposed on respective linear distal endportions of feeder lines belonging to the respective groups andextending in opposite directions that are 180° apart from each other.The planar array antenna elements 12a.sup.˜ 12h are arrayed in adirection perpendicular to the linear distal end portions of the feederlines.

Each of the eight MMICs 13a.sup.˜ 13h is composed of the transmittingand receiving assemblies of two adjacent transmitting and receivingchannels of the 16 transmitting and receiving channels A.sup.˜ P. Forexample, the MMIC 13a shown in FIG. 3 is composed of the selectivetransmission amplifier 15a, the selective reception amplifier 16a, andthe mixer 17a which belong to the transmitting and receiving assembly ofthe transmitting and receiving channel A, and the selective transmissionamplifier 15b, the selective reception amplifier 16b, and the mixer 17bwhich belong to the transmitting and receiving assembly of thetransmitting and receiving channel B.

The planar array antenna 12a, which is composed of rectangular patchesPa1, Pa2, of the transmitting and receiving channel A is connected tothe linear distal end portion of a feeder line FLa, whose proximal endportion is divided into a transmission end portion TXOUT and a receptionend portion RXIN by the circulator 14a. The rectangular patches Pa1, Pa2are spaced a certain distance along the linear distal end portion of thefeeder line FLa. The transmission end portion TXOUT separated by thecirculator 14a is connected through the selective transmission amplifier15a to an input terminal TXIN of the MMIC 13a for receiving an FM signalfrom the FM signal generator 23. The reception end portion RXINseparated by the circulator 14a is connected to an input terminal, i.e.,a received signal input terminal, of the mixer 17a. The other inputterminal, i.e., a local oscillator input terminal, of the mixer 17a isselectively supplied with an FM signal from the input terminal TXINthrough the selective reception amplifier 16a.

Similarly, the planar array antenna 12b, which is composed ofrectangular patches Pb1, Pb2, of the transmitting and receiving channelB is connected to the linear distal end portion of a feeder line FLb,whose proximal end portion is divided into a transmission end portionTXOUT and a reception end portion RXIN by the circulator 14b. Thetransmission end portion TXOUT separated by the circulator 14b isconnected through the selective transmission amplifier 15b to the inputterminal TXIN of the MMIC 13a for receiving an FM signal from the FMsignal generator 23. The reception end portion RXIN separated by thecirculator 14b is connected to an input terminal of the mixer 17b. Theother input terminal of the mixer 17b is selectively supplied with an FMsignal from the input terminal TXIN through the selective receptionamplifier 16b.

The selective transmission amplifiers 15a, 15b and the selectivetransmission amplifiers 16a, 16b of the transmitting and receivingchannels A, B are composed mainly of high-frequency FETs (field-effecttransistors). These four selective amplifiers 15a, 15b, 16a, 16bintermittently amplify supplied input signals in response to respectiveintermittent drain voltages Vd1.sup.˜ Vd4 selectively supplied from thechannel controller 22 of the main radar circuit 20. The four selectiveamplifiers 15a, 15b, 16a, 16b are also supplied with a constant gatevoltage Vg.

DC magnetic fields in mutually opposite directions are applied to thecirculators 14a, 14b, respectively, for rotating signals in mutuallyopposite directions in the circulators 14a, 14b. The application of DCmagnetic fields in mutually opposite directions to the circulators 14a,14b is effective to cancel those DC magnetic fields and prevent a DCmagnetic field from being generated.

FIG. 4 illustrates in perspective an FM radar system which incorporatesthe FM radar module 10 shown in FIG. 1. As shown in FIG. 4, the FM radarmodule 10 is housed in a metallic holder 40 and integrally combined witha secondary radiator 30 by the metallic holder 40, with the antennaassembly 12 serving as a primary radiator. The secondary radiator 30 hasa parabolic reflecting surface 30a, and the antenna assembly 12 composedof the 16 planar array antenna elements 12a.sup.˜ 12p is positioned inthe vicinity of the focal point of the parabolic reflecting surface 30a.FM signals in a millimeter wavelength range which are radiated from therespective planar array antenna elements 12a.sup.˜ 12p are reflected bythe parabolic reflecting surface 30a and radiated at respectivedifferent angles or bearings in a horizontal direction forwardly of thesecondary radiator 30. The primary radiator composed of the antennaassembly 12 and the secondary radiator 30 jointly make up an offsetmultiple-beam parabolic antenna.

In each of the planar array antenna elements 12a.sup.˜ 12p, the tworectangular patches are spaced a certain distance from each other alongthe linear distal end portion of the feeder line. Electromagnetic wavesare radiated at a certain tilt angle from the respective planar arrayantenna elements 12a.sup.˜ 12p. Specifically, as shown in FIG. 6, thedirection (indicated by the solid lines) in which the electromagneticwaves are radiated from the respective patches is inclined at a tiltangle relative to a line (indicated as the dot-and-dash line) normal tothe dielectric substrate 11 such that equiphase surfaces (indicated bythe dotted lines) of the electromagnetic waves radiated from therespective patches lie perpendicularly to the direction in which theyare radiated from the respective patches. The equiphase surfaces of theradiated electromagnetic waves are determined by a delay time which iscaused when the signals are propagated through the feeder lines and theelectromagnetic waves are propagated through the air.

While the patches are shown thicker than the feeder line in FIG. 6 fordistinguishing the patches from the feeder line, they are so shown forillustrative purpose only and are actually of the same thickness. Thelength of the feeder line portion that interconnects the two patches ofeach of the eight planar array antenna elements of one group issubstantially a half wavelength different from the length of the feederline portion that interconnects the two patches of each of the eightplanar array antenna elements of the other group so that theelectromagnetic waves will be radiated from the planar array antennaelements of the two groups at the same angle toward the secondaryradiator.

As shown in FIG. 4, since each of the planar array antenna elements12a.sup.˜ 12p radiates the electromagnetic wave at a tilt angle, asdescribed above, the FM radar module 10 which is large in size, whencompared with the primary radiator, is effectively prevented frominterfering with the electromagnetic waves radiated from the secondaryradiator 30. Accordingly, the FM radar module 10 that includes theantenna assembly 12 as the primary radiator can be positioned near thesecondary radiator 30. With this arrangement, the FM radar module 10 isallowed to be of an MMIC-based structure which is made up of the MMICs13a.sup.˜ 13h composed of the transmitting and receiving assemblies andthe antenna assembly 12 on the dielectric substrate 11.

Referring back to FIG. 1, the FM millimeter-wave signals supplied fromthe FM signal generator 23 are selectively amplified only in givenperiods successively by the respective selective transmission amplifiers15a.sup.˜ 15p in the respective transmitting and receiving channelsA.sup.˜ P according to channel control signals supplied from the channelcontroller 22. Each of the selective transmission amplifiers 15a.sup.˜15p comprises two cascaded FETs and switching transistors forintermittently supplying an operating drain voltage to the FETsaccording to the channel control signal, and selectively amplifies theFM millimeter-wave signal only in a period in which operating electricenergy is supplied thereto.

More specifically, unless a drain voltage is supplied, each of theselective transmission amplifiers 15a.sup.˜ 15p imparts a largeinsertion loss to the FM millimeter-wave signal passing therethrough,virtually separating the FM signal generator 23 and the correspondingone of the circulators 14a.sup.˜ 14p. Therefore, each of the selectivetransmission amplifiers 15a.sup.˜ 15p functions as a switch having sucha gain for selectively connecting the FM signal generator 23 to anddisconnecting the FM signal generator 23 from the corresponding one ofthe circulators 14a.sup.˜ 14p. The FM millimeter-wave signals amplifiedby the respective selective transmission amplifiers 15a.sup.˜ 15p aresupplied through the respective circulators 14a.sup.˜ 14p to therespective planar array antenna elements 12a.sup.˜ 12p, which thenradiate the FM millimeter-wave signals as electromagnetic waves awayfrom the dielectric substrate 11 toward the secondary radiator 30 (seeFIG. 4). The radiated electromagnetic waves are reflected by theparabolic reflecting surface 30a of the secondary radiator 30 out of themotor vehicle on which the FM radar system is installed.

Some of the FM millimeter-wave signals radiated as electromagnetic wavesout of the motor vehicle are reflected by objects, travel back to andare received by the planar array antenna elements 12a.sup.˜ 12p. Thereflected electromagnetic waves which are received by the planar arrayantenna elements 12a.sup.˜ 12p are separated as FM echo signals from thetransmitting channels by the circulators 14a.sup.˜ 14p, respectively.The separated FM echo signals are supplied to the respective receivedsignal input terminals of the mixers 17a.sup.˜ 17p. The other localoscillator input terminals of the mixers 17a.sup.˜ 17p are supplied withamplified FM millimeter-wave signals from the selective receptionamplifiers 16a.sup.˜ 16p which successively amplify FM millimeter-wavesignals intermittently only in given periods according to channelcontrol signals supplied from the channel controller 22. The selectivereception amplifiers 16a.sup.˜ 16p function as respective switches aswas the case with the selective transmission amplifiers 15a.sup.˜ 15p.

Beat signals outputted from respective output terminals of the mixers17a.sup.˜ 17p are transmitted through output terminals BTa, BTb to theselector 24. In the selector 24, the beat signals are amplified byrespective amplifiers 24a.sup.˜ 24b whose amplification factor variesdepending on the frequency. The amplifiers 24a.sup.˜ 24b are selected ina time-sharing fashion by the channel controller 22 to supply theamplified beat signals through a coaxial cable to the A/D converter 25,which converts the beat signals into digital beat signals. The digitalbeat signals are then supplied to the FFT circuit 26, and convertedthereby into a frequency spectrum that is then supplied to the CPU 21.

The CPU 21 analyzes the frequency spectrum of the received FM echosignals supplied from the FFT circuit 26, and calculates distances tothe objects which have produced the FM echo signals in the respectivetransmitting and receiving channels and hence at respective bearings.Typically, the CPU 21 generates a two-dimensional map of obstacles tothe motor vehicle as shown in FIG. 5.

FIG. 7 shows in plan a pattern of planar array antenna elements of an FMradar module according to another embodiment of the present invention.In the embodiment shown in FIG. 7, eight planar array antenna elements12a.sup.˜ 12h are divided into a group of four planar array antennaelements 12a.sup.˜ 12d and a group of four planar array antenna elements12e.sup.˜ 12h. The four planar array antenna elements 12a.sup.˜ 12d ofone group and the four planar array antenna elements 12e.sup.˜ 12h ofthe other group are disposed on respective linear distal end portions offeeder lines belonging to the respective groups and extending inopposite directions that are 180° apart from each other. The four planararray antenna elements 12a.sup.˜ 12d and the four planar array antennaelements 12e.sup.˜ 12h are positioned substantially in an end-to-endconfiguration, but are staggered with respect to each other in adirection across the feeder lines, i.e., are held out of alignment witheach other in a direction along the feeder lines. This arrangementpermits the planar array antenna elements to be transversely spaced atrelatively small intervals for small antenna size and high bearingresolution.

The present invention has been described above as being embodied as anFM radar module. However, the principles of the present invention arealso applicable to any of various other radar modules including an AMradar module, a pulse radar module, etc. Rather than employing the FMsignal generator 23 in the main radar circuit 20, a voltage-controlledoscillator of 60 GHz may be mounted in the form of an MMIC on thedielectric substrate 11, or included in each of the MMICs 13a.sup.˜ 13hon the dielectric substrate 11 for lower cost and smaller size.

The FM radar module according to the present invention offers thefollowing various advantages: Since the plurality of small-size planararray antenna elements are arrayed so as to be shared by thetransmitting and receiving assemblies through the circulators, thenumber of planar array antenna elements may be increased in a limitedinstallation space, making it possible to scan a relatively largeangular range with a scanning beam. The planar array antenna elementsserve as a primary radiator in an offset defocused multiple-beamparabolic antenna for wide scanning angular range and high bearingresolution.

Since the planar array antenna elements are combined with thecirculators so as to be shared by the transmitting and receivingassemblies, the various components of the antenna assembly 12 aremounted in a high-density configuration. Specifically, the selectivetransmission and reception amplifiers and the mixers in the form ofMMICs are mounted on the single dielectric substrate, making up theantenna assembly 12 serving as the primary radiator. An FM radar systemof the scanning type which incorporates the antenna assembly 12 is of ahigh-density structure, a small size, a low cost, and high resolution,suitable for use on motor vehicles. The FM radar system can be used in awide range of motor vehicle applications including an active cruisecontrol system, a collision prevention system, etc.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

What is claimed is:
 1. An antenna device comprising:a dielectricsubstrate; an array of antenna elements mounted on said dielectricsubstrate, each of said antenna elements comprising a plurality ofpatches interconnected in a direction transverse to said array; and aplurality of circulators mounted on said dielectric substrate andconnected in series to said antenna elements, respectively, wherein saidcirculators are arranged in pairs of adjacent circulators, saidcirculators in each of the pairs being arranged such that DC magneticfields in mutually opposite directions are applied to the circulators,respectfully, for rotating signals in mutually opposite directions inthe circulators.
 2. An antenna device according to claim 1, furthercomprising a scanning control circuit for switching the antenna elementsin a time-sharing fashion.